Biochemical
assessment of flavour of imported onions and onions grown in the UK
Hamish A Collin1, Tim Crowther2,
Meriel G Jones1, David E O'Connor3, Brian Smith2,
A Brian Tomsett1
1 School of Biological Sciences, Liverpool
University, Liverpool. L69 3BX. UK.
2 Horticulture Research International, Wellesbourne,
Warwick. CV35 9EF. UK.
3 Allium & Brassica Centre Ltd., Wash Rd, Kirton.
Boston. Lincs. PE20 1QQ.
Tel No 01517943612/3623 Fax 01517943655 e-mail
h.a.collin@liverpool.ac.uk
Abstract of poster presented at Alliums 2000,
Georgia USA 30 October - 4 November 2000
The marketing of onions in the UK is based on pungent
cooking onions, which are grown largely in the UK supplemented from Australia
and NZ, so called mild onions which are imported exclusively from Spain and
Chile, and very small volumes of sweet onions of the Vidalia type, imported from
the USA. At the moment the classification of these different types is based on
source rather than on the strength of their flavour. In onions flavour is
dependent on the concentration and type of a limited number of flavour
precursors in the bulb. These are degraded by an enzyme alliinase when the
tissue is damaged so releasing the volatiles. The aim of the project was to
establish a biochemical method for assessing flavour in commercial onions and in
those used in plant breeding trials so as to have a less arbitrary test. Store
onions have been assessed for flavour using the flavour precursors as a
quantitative measure, as well as new genotypes under trial in the UK
environment, and exposed to local soil type, additional soil sulphur and long
term storage. Flavour precursors were measured directly by HPLC and indirectly
by the pyruvate test.
Molecular
markers for Sclerotium cepivorum, white rot disease of onion.
Meriel G Jones, M. Anwar Haq, A Brian Tomsett and Hamish
A Collin
School of Biological Sciences, Liverpool University,
Liverpool. L69 3BX. UK.
Tel No 01517943612/3623 Fax 01517943655 email
h.a.collin@liverpool.ac.uk
Abstract of poster presented at Alliums 2000, Georgia USA 30 October - 4 November 2000
White rot, caused by the fungus Sclerotium cepivorum, is a serious disease of onions. It attacks the plants progressively during the growing season, and can persist in the soil in resistant survival structures (sclerotia) for decades. At early stages of infection, however, it is difficult to distinguish infected from non-infected onion seedlings. We have been carrying out a combined molecular biological and electron microscopic study to detect early infections in young onion seedlings. Electron microscopy shows that hyphae surround the seedling and invade through successive layers of onion tissue. We have optimised primers and reaction conditions in the polymerase chain reaction to detect a ribosomal ITS sequence from S. cepivorum in the presence of a large excess of plant DNA. The primers are based on sequences in ITS1 and ITS2, which show maximum differences from the sequence of closely related fungi. The specificity of amplification was tested and was specific to S. cepivorum, in that related fungi were not amplified. Conversely, DNA from a number of independent S. cepivorum isolates from different sites within the UK could all be amplified. S. cepivorum was detected in both young, laboratory-infected seedlings and field-grown mature bulbs.
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